Method of insulating stem pins of a cathrode ray tube

ABSTRACT

A method of insulating a cathode ray tube and enabling an electrical insulator to be produced without material loss and enabling improvement of the bonding strength between a stem and a stem base, which comprises a base through which pin through holes are formed and has provided projecting from the front surface thereof a tip holder, in a state with the stem pins inserted through the pin through holes and the tip held in the tip holder, said method comprising the steps of molding an electrical insulator composition comprising an uncured self-adhesive silicone rubber into a predetermined sheet shape by using a transfer mold to obtain an electrical insulator, arranging the electrical insulator in a state extending from the positions of the pin through holes on the back of the base of the stem base to the tip holder and adhering it to the back of the base, folding the portion of the electrical insulator extending to the tip holder to the inside surface of the tip holder, and attaching the stem base to the stem.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of insulating a cathode raytube used for electrical equipment having high voltage electrodes, inparticular color television receivers, video and computer monitors,etc., applied to the insulation between stem pins to which a highvoltage is supplied and to an electrical insulator composition for acathode ray tube used for insulation between high voltage stem pins of acathode ray tube and between other electrodes to which a high voltage issupplied.

2. Description of the Related Art

Generally, as shown in FIGS. 1B and 1C, a stem 20 is integrally attachedto a neck of a cathode ray tube by fusing together the glass at isperiphery and the glass around the end edge of the neck 1a. A stem base30 is attached to the stem 20. The stem 20 is provided with a pluralityof stem pins 21 at its periphery serving as electrodes in apredetermined pin circle shape and with a tip 22 projecting from itscenter portion. Note that the illustration of the stem pins 21 isomitted in FIG. 1C.

The stem base 30 is made of a polycarbonate or other plastic having anexcellent insulating property and comprises, as shown in FIGS. 1A, 1B,and 2, a circular base 31, a tip holder 32 provided at the centerportion of the base 31 for holding the tip 22 of the stem 20, asector-shaped stem pin holder 33 provided on the base 31 in a state alsoserving as a part of a side wall of the tip holder 32 for holding thehigh voltage stem pins 21, and a skirt portion 34 extending downwardfrom the peripheral edge of the base 31. The base 31 is formed,corresponding to the stem pins 21, with pin through holes 35 throughwhich the stem pins 21 are inserted at the time of attaching the stembase 30 to the stem 20.

As a method of the related art for electrical insulation between thestem pins 21 of the stem 20 to which the stem base 30 is attached, amethod of interposing an electrical insulator 40 shown in FIGS. 3A and3B between the stem 20 and the stem base 30 as shown in FIG. 1B isknown. The electrical insulator 40 is formed as a thick disk shape andis formed at its center portion with a tip through hole 41 for insertingthe tip 22 of the stem 20. Further, pin through holes 42 through whichall of the stem pins 21 including the high voltage stem pins areinserted at the time of placing the electrical insulator 40 on the stem20 are formed corresponding to the stem pins 21.

The electrical insulator 40 is prepared by, for example in JapaneseUnexamined Patent Publication (Kokai) No. 8-111191, extruding into atape shape a viscous electrical insulator composition comprising 100parts by weight of a silicone compound having an electrical insulationproperty plus 2 parts by weight of a silane coupling agent and 1.5 partsby weight of an organic peroxide (hereinafter referred to as the"insulator composition") and punching out a disk shape using a die set.Further, Japanese Unexamined Patent Publication (Kokai) No. 7-94100discloses a method of obtaining an electrical insulator by molding aviscous insulator comprising a silicone compound similar to the abovepublication into a flat plate of a large area and punching out diskshapes by a molding tool.

In both publications, first, the electrical insulator 40 shown in FIG.4A is adhered to the back of the base 31 of the stem base 30 shown inFIG. 4B as shown in FIG. 4C. Then, the stem pins 21 are inserted throughthe pin through holes 42 of the electrical insulator 40 and the pinthrough holes 35 of the stem base 30 and the tip 22 is inserted throughthe tip through hole 41 of the electrical insulator 40 and the tipholder 32 of the stem base 30. In that state, the stem base 30 isattached to the stem 20 of the cathode ray tube 1, then pressed andheated to bond it so as to achieve electrical insulation between thestem pins 21.

Summarizing the problems to be solved by the present invention, in theinventions disclosed in Japanese Unexamined Patent Publication (Kokai)Nos. 8-111191 and 7-94100, however, since both punch out disk shapesfrom an insulator composition of a tape shape or a flat plate shape by adie set or a molding tool, the portion remaining after punching becomeswasted, that is, there is a disadvantage of a loss of the material loss.

Also, because the disk is produced by punching, it is difficult to moldthe electrical insulator into a shape corresponding to a complicatedlyshaped stem or stem base of a cathode ray tube. As a result, it ends upallowing air to become entrained between the stem base and the stem atthe time of attaching the two. When air is entrained, disadvantages arecaused such as a decline in the insulation property between the stempins 21 due to the entrained air, an inability to draw out 100% of theelectrical characteristics of the cathode ray tube, and insufficientbonding force between the stem and the stem base.

Note that since it is difficult to mold an electrical insulator into acomplicated shape in the related art as explained above, an electricalinsulator of substantially the same size as the base of the stem basehas been prepared to provide insulation between all stem pins projectingfrom the stem. However, in actuality, it is possible to achievesufficient electrical characteristics of the cathode ray tube by justinsulation between the high voltage stem pins among the plurality ofstem pins.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of insulatinga cathode ray tube enabling production of an electrical insulatorwithout loss by efficiently using the electrical insulator composition.

Another object of the present invention is to provide a method ofinsulating a cathode ray tube enabling easy molding of an electricalinsulator into a shape corresponding to a complicatedly shaped stem andstem base of the cathode ray tube by transfer molding and therebyenabling attachment of the stem base to the stem without entrainment ofair.

A still other object of the present invention is to provide anelectrical insulator composition for a cathode ray tube which is veryeffective in realizing a cathode ray tube improved in bonding of thestem and the stem base and improved in the insulation property betweenthe high voltage stem pins by the above method of insulating a cathoderay tube.

According to a first aspect of the present invention, there is provideda method of insulating a cathode ray tube for insulation between stempins using an electrical insulator when attaching to a stem, which isprovided at the cathode ray tube and has a tip and stem pins projectingtherefrom, an insulating stem base, which comprises a base through whichpin through holes are formed and has provided projecting from the frontsurface thereof a tip holder, in a state with the stem pins insertedthrough the pin through holes and the tip held in the tip holder,comprising the steps of molding an electrical insulator compositioncomprising an uncured self-adhesive silicone rubber into a predeterminedsheet shape by using a transfer mold to obtain an electrical insulator,arranging the electrical insulator in a state extending from thepositions of the pin through holes on the back of the base of the stembase to the tip holder and adhering it to the back of the base, foldingback the portion of the electrical insulator extending to the tip holderto the inside surface of the tip holder, and attaching the stem base tothe stem.

According to the above aspect of the present invention, since anelectrical insulator composition is molded by using a transfer mold(hereinafter the molding will be referred to as "transfer molding") toobtain an electrical insulator, there is no loss of the electricalinsulator composition such as when obtaining an electrical insulator byusing a die set or molding tool. Also, due to the transfer molding, itbecomes possible to easily mold the electrical insulator into a shapecorresponding to the complicatedly shaped stem and stem base of thecathode ray tube. Further, since the electrical insulator is arranged ina state extending from the positions of the pin through holes toward thetip holder when adhering it to the back of the base of the stem base,and since the portion of the electrical insulator extending to the tipholder is folded back to the inside surface of the tip holder prior toattaching the stem base to the stem, the entrainment of air can besuppressed at the time of attaching the stem base to the stem.

According to a second aspect of the present invention, there is providedan electrical insulator composition for a cathode ray tube comprising anuncured self-adhesive silicone rubber, wherein the uncured self-adhesivesilicone rubber comprises, with respect to 100 parts by weight of asilicone compound, 0.001 to 15 parts by weight of a bonding aid and 0.01to 5 parts by weight of a vulcanization agent and has a Williamsplasticity adjusted to 100 to 300.

According to the above aspect of the present invention, since 0.001 to15 parts by weight of a bonding aid is added to the silicone compound,an electrical insulator composition achieving a bondability effectivelyand having an excellent releasability from the transfer mold when usedfor transfer molding can be obtained. Also, since 0.01 to 5 parts byweight of a vulcanization agent is added, an electrical insulatorcomposition having an excellent rubber strength and enabling work usingthis electrical insulator composition to be performed with good workefficiency is obtained. Furthermore, since the composition is adjustedto a Williams plasticity of 100 to 300, the releasability from thetransfer mold is excellent when using the electrical insulatorcomposition for transfer molding and the composition can be easilymolded into a complicated shape. Accordingly, an electrical insulatorcomposition comprising a silicone compound to which an adhesive andvulcanization agent are added in the above ranges has an excellentreleasability from a transfer mold, is easily molded into a complexshape, is easy to handle and is otherwise extremely suited to transfermolding, and has an excellent rubber strength.

According to a third aspect of the present invention, there is providedan electrical insulator composition for a cathode ray tube comprising anuncured adhesive silicone rubber, wherein the uncured adhesive siliconerubber comprises, with respect to 100 parts by weight of a siliconecompound, 0.001 to 15 parts by weight of a bonding aid, 0.1 to 10 partsby weight of a cross-linking agent, and 0.0001 to 1 part by weight of aplatinum compound and has a Williams plasticity adjusted to 100 to 300.

According to the above aspect of the present invention, since 0.001 to15 parts by weight of a bonding aid is added to the silicone compound,an electrical insulator composition achieving a bondability effectivelyand having an excellent releasability from the transfer mold when usedfor transfer molding can be obtained. Also, since 0.1 to 10 parts byweight of a cross-linking agent is added, an electrical insulatorcomposition having a predetermined hardness and an excellent insulationproperty can be obtained and, since 0.0001 to 1 part by weight of aplatinum compound is added, an electrical insulator composition whichcures by a suitable curing rate can be obtained. Further, since thecompound is adjusted to a Williams plasticity of 100 to 300, thereleasability from the transfer mold is excellent when using theelectrical insulator composition for transfer molding and thecomposition can be easily molded into a complicated shape. Accordingly,an electrical insulator composition comprising a silicone compound towhich bonding aid, cross-linking agent, and platinum compound are addedin the above ranges has an excellent releasability from a transfer mold,is easily molded into a complex shape, is extremely suited to transfermolding, cures at a suitable curing rate, and has an excellentinsulation property.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clearer from the following description of the preferredembodiments given with reference to the accompanying drawings, in which:

FIGS. 1A to 1C are views of a neck of a cathode ray tube of the relatedart where insulation is provided between stem pins, wherein FIG. 1A is aperspective view, FIG. 1B is a sectional view along the line E--E inFIG. 1A, and FIG. 1C is a sectional view of the stem;

FIG. 2 is a perspective view of an example of a stem base of the relatedart:

FIGS. 3A and 3B are views of an example of an electrical insulator ofthe related art, wherein FIG. 3A is a perspective view and FIG. 3B is asectional view along the line F--F in FIG. 3A;

FIGS. 4A to 4C are views for explaining a method of insulating a cathoderay tube of the related art, wherein FIG. 4A is a perspective view of anelectrical insulator, FIG. 4B is a perspective view of a stem base, andFIG. 4C is a perspective view of a state where the electrical insulatoris attached to the stem base;

FIGS. 5A to 5D are views for explaining a molding step in a method ofinsulating a cathode ray tube according to an embodiment of the presentinvention, wherein FIG. 5A is a sectional view of a transfer mold at thetime of molding, FIG. 5B is a plan view of the transfer mold in anopened state in the plane shown by the line A--A of FIG. 5A, FIG. 5C isa plan view of FIG. 5B in a state with one of the two mandrels in FIG.5B removed, and FIG. 5D is a plan view of an electrical insulator takenout from the transfer mold;

FIGS. 6A and 6B are views of an electrical insulator obtained by themolding step according to the embodiment, wherein FIG. 6A is aperspective view and FIG. 6B is a sectional view along the line B--B inFIG. 6A;

FIGS. 7A to 7C are explanatory views of an adhering step and a foldingstep according to the embodiment, wherein FIG. 7A is a perspective viewof a stem base and FIGS. 7B and 7C are views of FIG. 7A from thedirection of the line C in the adhering step and the folding step; and

FIGS. 8A and 8B are views of the attaching step of the stem base to astem, wherein FIG. BA is a perspective view and FIG. 8B is a sectionalview along the line D--D in FIG. 8A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Below, preferred embodiments of a method of insulating a cathode raytube and an electrical insulator composition of a cathode ray tube ofthe present invention will be described based on the accompanyingdrawings.

FIRST EMBODIMENT

First, prior to the explanation of the method of insulating a cathoderay tube of an embodiment of the present invention for insulatingbetween stem pins of a stem provided at a neck of the cathode ray tubeby providing an electrical insulator between the stem and the stem baseattached thereto, an explanation will be given of an electricalinsulator composition (hereinafter, referred to as an "insulatorcomposition") of the electrical insulator used in the embodiment.

The insulator composition according to the present invention iscomprised of an uncured self-adhesive silicone rubber used for transfermolding. An insulator composition of a first embodiment is comprised byadding 0.001 to 15 parts by weight of a bonding aid and 0.01 to 5 partsby weight of a vulcanization agent to 100 parts by weight of the uncuredadhesive silicone rubber and has a Williams plasticity adjusted to 100to 300.

As the above silicone compound, specifically a diorganopolysiloxane ofthe following average composition formula (1) to which various fillers,additives, and pigments have been added can be used.

    R.sub.n SiO.sub.(4-n)/2                                    (1)

where, R indicates a substituted or unsubstituted monovalent hydrocarbongroup and n is a positive value from 1.95 to 2.05.

Here, in the above formula (1), R is preferably a substituted orunsubstituted C₁ to C₁₀ monovalent hydrocarbon group, specifically, amethyl group, ethyl group, propyl group, or other alkyl group, acyclopentyl group, cyclohexyl group, or other cycloalkyl group, a vinylgroup, allyl group, or other alkenyl group, a cycloalkenyl group, phenylgroup, tolyl group, or other aryl group, or a halogenated hydrocarbongroup or cyanated hydrocarbon group comprised of these groups withhydrogen atoms partially substituted by a chlorine atom or cyano groupor other organic group.

Generally, as a silicone compound, one where the backbone of the abovediorganopolysiloxane is comprised of dimethylpolysiloxane units, onewhere the backbone of the above dimethylpolysiloxane has a phenyl group,vinyl group, γ-trifluoropropyl group, etc. introduced, etc. aresuitable. Note that the polymerization degree of thediorganopolysiloxane is preferably 100 or more, more preferably 300 to10,000. This is because if the polymerization degree is less than 100,the mechanical strength of the cured silicone compound declines and themoldability becomes poor in some cases, while if it exceeds 10,000, thefluidity of the silicone compound declines and the moldability becomespoor in some cases.

As the various fillers, additives, pigments, etc. able to be added tothe diorganopolysiloxane, for example, silica hydrogel (hydrous silicicacid), silica aerogel (anhydrous silicic acid-fumed silica), and otherreinforcing silica fillers, clay, calcium carbonate, diatomaceous earth,titanium dioxide, and other fillers, low molecular siloxane esters (forexample, dimethylsilane dimethylester), silanol (for example,diphenylsilanediol), and other dispersants, iron oxide, cerium oxide,iron octylate, and other agents for improving heat resistance, platinumcompounds for imparting fire retardance, etc. may be mentioned. Thesemay be added to and mixed with the diorganopolysiloxane alone or incombinations of two or more types in accordance with need in the usualamounts.

The bonding aid, a component of the insulator composition of the firstembodiment, is an important component for making the electricalinsulator formed from the insulator composition as explained later bondwith the glass cathode ray tube, metal stem pins, and plastic stem base.As a bonding aid, for example, ones of the chemical formulas (2) to (12)below are used: ##STR1##

The amounts of these bonding aids added differ depending on the type ofthe bonding aid used, but normally, as mentioned earlier, 0.001 to 15parts by weight is added with respect to 100 parts by weight of thesilicone compound. The amount was made at least 0.001 part by weightsince the effect of bonding is not sufficiently manifested when lessthan 0.001 part by weight is added. Further, the upper limit of theamount added was made 15 part by weight since the bonding strength doesnot change even if more than 15 parts by weight and, moreover,disadvantages arise in the processability, for example, problems arisein the releasability from the transfer mold used in the later explainedmolding step. More preferably, 0.01 to 10 parts by weight may be addedwith respect to 100 parts by weight of the silicone compound.

The vulcanization agent, another component of the insulator compositionof the first embodiment, is added to make the silicone compound cure. Asthe vulcanization agent, for example, an organic peroxide is used. Inparticular, a diacyl peroxide is preferable. As examples of a diacylperoxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide,m-methylbenzoyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoylperoxide, octanoyl peroxide, decanoyl peroxide, lauryl peroxide, etc.may be mentioned. Among these, use of p-methylbenzoyl peroxide ando-methylbenzoyl peroxide, which make the work efficiency excellent sincethey enable ordinary pressure steam vulcanization, is optimal. At thistime, it is possible to use either one of the p-methylbenzoyl peroxideand o-methylbenzoyl peroxide or possible to add both as thevulcanization agent.

The amount of the vulcanization agent added is preferably, as mentionedabove, 0.01 to 5 parts by weight with respect to 100 parts by weight ofthe silicone compound. This range is made preferable because if lessthan 0.01 part by weight, the vulcanization becomes insufficient and therubber strength declines, while if more than 5 parts by weight, theresultant insulator composition cures too fast and the work efficiencyin the series of steps for insulating the cathode ray tube declines.

When producing the insulator composition, the silicone compound plus thebonding aid and vulcanization agent are kneaded by a twin-roll or otherkneader. By doing this, an insulator composition of a cathode ray tubecomprised of an uncured self-adhesive silicone rubber can be obtained.At this time, it is preferable that the Williams plasticity of theinsulator composition be adjusted to 100 to 300. This is because if theWilliams plasticity is less than 100, the releasability from thetransfer mold is poor, while if the Williams plasticity exceeds 300,though the releasability from the transfer mold is good, molding into acomplicated shape becomes difficult.

As explained above, the insulator composition of the first embodiment isone comprised of a silicone compound to which is added a bonding aid ina range where the bondability is effectively manifested and thereleasability from the transfer mold used in the molding step isexcellent and is one to which is added a vulcanization agent in a rangewhere the rubber strength is good and the series of steps for insulatingthe cathode ray tube can be performed with a good work efficiency.Further, since the Williams plasticity is adjusted to a Williamsplasticity giving a good releasability from the transfer mold andenabling easy molding into a complex shape, the composition is extremelysuited to transfer molding.

Therefore, according to the first embodiment, an insulator compositionis obtained which enables an electrical insulator having an excellentrubber strength and of a desired shape for insulating the cathode raytube to be easily obtained by the transfer molding step and whichenables the transfer molding step and the following folding step etc. tobe carried out with a good work efficiency.

SECOND EMBODIMENT

An insulator composition comprised of an uncured self-adhesive siliconerubber of the second embodiment differs from that of the firstembodiment in that instead of a vulcanization agent, a cross-linkingagent, a platinum compound, and a control agent are added. That is, itis comprised of 0.001 to 15 parts by weight of bonding aid, 0.1 to 10parts by weight of a cross-linking agent, 0.0001 to 1 part by weight ofa platinum compound, and not more than 1 part by weight of a controlagent added with respect to 100 parts by weight of the silicone compoundand has a Williams plasticity adjusted to 100 to 300.

As the above cross-linking agent, for example, a polysiloxane having ahydrogen atom bonded with a silicon atom in its molecule may bementioned. As examples, there are the organohydrogen polysiloxanes ofthe following chemical formulas (13) and (14). ##STR2##

The amount of this cross-linking agent added is, as mentioned above,preferably 0.01 to 10 parts by weight with respect to 100 parts byweight of the silicone compound. This is because if less than 0.01 partby weight, the composition does not cure to the necessary hardness,while if over 10 parts by weight, bubbles etc. occur in the insulatorcomposition and the insulation property declines--which isdisadvantageous in obtaining an electrical insulator for insulating ahigh voltage.

The above platinum compound, a component of the insulator composition ofthe second embodiment, acts as a catalyst for an addition reaction ofhydrogen to the vinyl group of the silicone compound and theorganohydrogen polysiloxane and is comprised of, for example,chloroplatinic acid and its derivatives. Preferably, the amount addedis, as explained above, 0.0001 to 1 part by weight with respect to 100parts by weight of the silicone compound. This range is preferablebecause if less than 0.0001 part by weight, the curing becomes slowerand the curability otherwise becomes poor resulting in time required forthe curing and even if more than 1 part by weight, the curability doesnot change, so there is a cost disadvantage.

As the control agent, another component of the insulator composition ofthe second embodiment, for example acetylene alcohol and followingchemical formula (15) are typical. As explained above, not more than 1part by weight with respect to 100 parts by weight of the siliconecompound is suitable. This is because when more than 1 part by weight,the curing becomes slower and disadvantages arise like the workefficiency in the series of steps in the method of insulating thecathode ray tube, in particular, the releasability from the transfermold, becomes poor. Note that the control agent is an optionalcomponent. Therefore, it is possible to configure the insulatorcomposition by eliminating the control agent from the insulatorcomposition of the second embodiment. However, by adding a controlagent, there are the advantages that the curing time can be adjusted,the durability can be increased, and furthermore long-term storagebecomes possible. ##STR3##

When producing the insulator composition of the second embodiment aswell, by kneading the silicone compound plus the bonding aid,cross-linking agent, platinum compound, and control agent by a twin-rollor other kneader, an insulator composition is obtained comprising anuncured self-adhesive silicone rubber in which the Williams Plasticityis adjusted to 100 to 300.

The insulator composition of the second embodiment configured in thisway is one comprised of a silicone compound to which is added across-linking agent in a range giving the desired hardness and anexcellent insulation property and is one to which a platinum compound isadded in a range enabling curing at a suitable curing rate and to whicha control agent is added in a range not affecting the curing rate andthe release from the transfer mold. Further, in the insulatorcomposition of the second embodiment as well, since the composition isadjusted to a Williams plasticity giving an excellent releasability fromthe transfer mold and enabling easy molding to a complex shape, thecomposition is extremely suited to transfer molding.

Therefore, according to the second embodiment, a insulator compositionis obtained which cures at a suitable curing rate and is excellent ininsulation property and which enables an electrical insulator of adesired shape for insulating the cathode ray tube to be easily obtainedby the transfer molding step and enables the transfer molding step andthe subsequent folding step etc. to be performed with a good workefficiency.

THIRD EMBODIMENT

Next, an embodiment of a method of insulating a cathode ray tubeaccording to the present invention will be explained based on a methodof insulating a cathode ray tube using an electrical insulator comprisedof the insulator composition of the first and second embodiments.

In the method of the present invention, first, as shown in FIG. 5, amolding step is carried out for obtaining an electrical insulator byusing a transfer mold to mold the insulator composition of the first andsecond embodiments into a predetermined sheet shape.

FIGS. 5A to 5D are views for explaining the molding step of the methodof insulating a cathode ray tube according to the embodiment. FIG. 5A isa sectional view of a transfer mold during the molding, FIG. 5B is aplan view of the transfer mold in an opened state in the plane shown bythe line A--A in FIG. 5A, FIG. 5C is a plan view of a state with one ofthe two mandrels in FIG. 5B removed, and FIG. 5D is a plan view of anelectrical insulator taken out from the transfer mold. FIGS. 6A and 6Bare views of an electrical insulator obtained by the molding stepaccording to the first embodiment. FIG. 6A is a perspective view, andFIG. 6B is a sectional view along the line B--B in FIG. 6A.

As shown in the figures, the transfer mold 50 is configured providedwith a plunger mold 51, a pot mold 52, a mandrel 53, and a lower mold54. The lower mold 54 and the mandrel 53 arranged above it form a cavitycorresponding to the outer shape of an electrical insulator 10 to bemolded. The mandrel is configured by a combination of a pair of left andright mandrel parts 53a and 53b.

At the top side of the pot mold 52 arranged above the mandrel is formeda concave pot 52a to which the insulator composition 10 is supplied.Further, a sprue 52b serving as an injection path for the insulatorcomposition 10a is formed at the pot mold 52 in a state reaching fromthe pot 52a to the cavity 55 of the mandrel 53. An end of the sprue 52bopening at the lower surface of the pot mold 52 becomes a gate 52c andenables the insulator composition 10a to be injected into the cavity 55.Further, the lower portion of the plunger mold 51 arranged above the potmold 52 is provided with a plunger 51a of a shape substantially fittingwith the pot 52a.

When molding the electrical insulator 10 using such a transfer mold 50,first a release sheet 2 of an area sufficiently covering the cavity 55is arranged between the lower mold 54 and the mandrel 53 and the potmold 52 is arranged above the mandrel 53. The release sheet 2 iscomprised of, for example, a plastic film, is provided at one side ofthe obtained electrical insulator 10, and is removed at the time ofadhering the electrical insulator 10 to a stem base as explained below.The sheet 2 is also designed to prevent deformation when taking out themolded electrical insulator 10 from the transfer mold.

Next, the insulator composition 10a which is heated in advance forlowering its viscosity is charged into the preheated pot 52a, theplunger mold 51 is pushed down, and the insulator composition 10a istherefore injected into the cavity 55 from the pot 52a via the sprue 52band the gate 52c. Then, after holding this for a predetermined time tocause it to cure, the shaped article of the insulator composition 10a,that is, an electrical insulator 10, is taken out from the transfer mold50. One side of the electrical insulator 10 is provided with the releasesheet 2 as shown in FIG. 5D and FIGS. 6A and 6B.

Here, as an example of the electrical insulator 10, one for insulatingbetween two adjoining stem pins to which a high voltage is applied,among a plurality of stem pins provided on the stem, is molded. Also,part of the electrical insulator 10 is to be folded in the latermentioned folding step to the inside surface of the tip holder of thestem in the state with the other part adhered to a base of the stembase.

Therefore, the electrical insulator 10 is molded to a substantialY-shape in a plan view comprised of a folding portion 11 of asubstantially rectangular shape in a plan view and an adhesive portion12 branched into two from one end. The folding portion 11 to be foldedto the inside surface of the tip holder and the part of the adheringportion 12 close to its trunk are molded to a state with the approximatecenter in the lateral direction bulging out further than its two sidesas shown in FIG. 6B so that the folded portion will match with thecurved inside surface of the tip holder.

After obtaining the electrical insulator 10 in this way, an adheringstep for adhering the adhering portion 12 of the electrical insulator 10to the back of the base of the stem base and a folding step for foldingthe folding portion 11 of the electrical insulator 10 to the insidesurface of the tip holder are performed. FIGS. 7A to 7C are explanatoryviews of the adhering step and the folding step according to anembodiment. FIG. 7A is a perspective view of the stem base, while FIGS.7B and 7C are back views of FIG. 7A seen from the C line direction. Notethat for the stem base 30, one structured in the same way as that in therelated art shown in FIG. 2 is used, therefore the same components aregiven the same reference numerals in FIGS. 7A to 7C and explanationsthereof are omitted.

Namely, in the adhering step, as shown in FIG. 7B, the adhering portion12 of the electrical insulator 10 is adhered to the back of the base 31of the stem base 30 with the release sheet 2 facing up. At this time,the adhering portion 12 of the electrical insulator 10 is arranged atpositions of predetermined pin through holes 35 through which highvoltage use stem pins will be inserted, the folding portion 11 isarranged in a state extending to the tip holder 32 of the stem base 30,and the adhering portion 12 is adhered to the positions of thepredetermined pin through holes 35 in this state. At the time ofadhesion, a predetermined pressure is applied to the electricalinsulator 10 from above the sheet 2 to make it fit tight against thestem base 30. Then, the sheet 2 is peeled off.

Next, the electrical insulator 10 is pressed to straighten out itsshape. By straightening out its shape, the subsequent folding step canbe more easily performed and the folding portion 11 of the electricalinsulator 10 can be reliably arranged at the desired position. Then, asshown in FIG. 7C, the folding step for folding the folding portion 11 ofthe electrical insulator 10 extending to the tip holder 32 of the stembase 30 to the inside surface of the tip holder 32 is performed.

Then, the attaching step for attaching the stem base 30 to which theelectrical insulator 10 is adhered to the stem is performed. FIGS. 8Aand 8B are views of the state of the stem base 30 attached to the stem.FIG. 8A is a perspective view, while FIG. 8B is a sectional view alongthe line D--D in FIG. 8A. As a stem, one configured in the same way asin the related art shown in FIGS. 1B and 1C and attached to the neck 1aof the cathode ray tube 1 is used, so the same components are given thesame reference numerals in FIGS. 8A and 8B and explanations thereof areomitted.

At the time of attaching the stem base 30 to the stem 20, the stem pins21 of the stem 20 are inserted through the pin through holes 35 of thestem base 30 and the tip 22 is held in the tip holder 32. Also, highvoltage use stem pins 21 are made to be held in the stem pin holder 33.After the attachment, the stem base 30 is bonded and secured to the stem20 by heating. As a result of the above step, insulation is achievedbetween the high voltage use stem pins 21 on the stem 20 of the cathoderay tube 1.

In this way, in the present embodiment, since the electrical insulator10 is obtained by transfer molding the insulator composition 10a, thedisadvantage of material loss does not occur unlike the related art forobtaining an electrical insulator by using a die set or molding tool.Further, due to the transfer molding, the electrical insulator 10 can beeasily produced in a shape matching with the complicated shapes of thestem 20 and stem base 30 of the cathode ray tube 1.

Further, at the time of adhering the electrical insulator 10 to the backof the base 31 of the stem base 30, since the folding portion 11 isarranged in a state extending from the positions of the pin throughholes 35 to the tip holder 32 and since the folding portion 11 of theelectrical insulator 10 extending to the tip holder 32 is folded to theinside surface of the tip holder 32 prior to attaching the stem base 30to the stem 20, entrainment of air can be suppressed when attaching thestem base 30 to the stem 20. Accordingly, it is possible to prevent theinsulation property between the stem pins 21 from declining due to theentrained air, therefore the electrical characteristics can be broughtout 100 percent and a cathode ray tube 1 of a high reliability improvedin the bonding strength of the stem 20 and the stem base 30 can berealized.

Below, examples and a comparative example will be explained.

EXAMPLE 1

0.5 part by weight of the bonding aid shown in the above formula (2) wasadded to 100 parts by weight of a silicone compound (75 parts by weightof methylvinyl polysiloxane comprised of 99.85 mol % of dimethylsiloxaneand 0.15 mol % of methylvinylsiloxane and having an averagepolymerization degree of 8000 and 25 parts by weight of fumed silicasurface treated by hexamethyl disilazane and having a specific surfacearea of 200 m² /g), 1.3 parts by weight of p-methylbenzoyl peroxide wasblended in as a vulcanization agent, and the mixture was kneaded by atwin-roll to obtain an insulator composition for a cathode ray tube. TheWilliams plasticity of the composition was 200.

This insulator composition was molded into the shape of FIG. 6 bytransfer molding, whereupon an electrical insulator could be obtainedwithout any material loss due to generation of waste etc. Subsequently,the adhering portion of the electrical insulator was adhered to the stembase, then the electrical insulator was pressed to straighten out itsshape, the folding portion extending to the tip holder of the stem wasfolded to the inside surface of the tip holder, then the stem base wasattached to the stem of the cathode ray tube, this was pressed by apressing force of 1 MPa, and the entire cathode ray tube was heated in aheating chamber at 100° C. for 10 minutes to bond and secure the stembase to the stem to achieve insulation between the high voltage use stempins. The bonding strength of the stem base to the stem at this time wasa high 3 MPa. Further, voltage was applied across the high voltage usestem pins to test the insulation withstand voltage. As a result, theinsulation breakdown voltage was 35 kV. There was no loss of theinsulator composition.

EXAMPLE 2

1.0 part by weight of the bonding aid shown in the above formula (12)was added to 100 parts by weight of a silicone compound (76 parts byweight of methylvinyl polysiloxane comprised of 99.85 mol % ofdimethylsiloxane and 0.15 mol % of methylvinylsiloxane and having anaverage polymerization degree of 8000, 20 parts by weight of fumedsilica surface treated by hexamethyl disilazane and having a specificsurface area of 200 m² /g, 2 parts by weight of bengara, and 2 parts byweight of carbon black), 2 parts by weight of the cross-linking agentshown in the above formula (14), 0.01 part by weight of chloroplatinicacid as a platinum compound, and 0.005 part by weight of the controlagent shown in the above formula (15) were blended in, and the mixturewas kneaded by a twin-roll to obtain an insulator composition for acathode ray tube. The Williams plasticity of the composition was 250.

This insulator composition was molded into the shape of FIG. 6 bytransfer molding, whereupon an electrical insulator could be obtainedwithout any material loss due to generation of waste etc. Subsequently,the adhering portion of the electrical insulator was adhered to the stembase, then the electrical insulator was pressed to straighten out itsshape, the folding portion extending to the tip holder of the stem wasfolded to the inside surface of the tip holder, then the stem base wasattached to the stem of the cathode ray tube, this was pressed by apressing force of 1 MPa, and the entire cathode ray tube was heated in aheating chamber at 90° C. for 20 minutes to bond and secure the stembase to the stem to achieve insulation between the high voltage use stempins. The bonding strength of the stem base to the stem at this time wasa high 3.5 MPa. Further, voltage was applied across the high voltage usestem pins to test the insulation withstand voltage. As a result, theinsulation breakdown voltage was 35 kV. There was no loss of theinsulator composition.

COMPARATIVE EXAMPLE

2.0 parts by weight of γ-glycidoxypropyl-trimethoxysilane was added to100 parts by weight of a silicone compound (75 parts by weight ofmethylvinyl polysiloxane comprised of 99.85 mol % of dimethylsiloxaneand 0.15 mol % of methylvinylsiloxane and having an averagepolymerization degree of 8000 and 25 parts by weight of fumed silicasurface treated by hexamethyl disilazane and having a specific surfacearea of 200 m² /g), 1.5 parts by weight of 2,4-dichlorobenzoyl peroxidewas blended in as a vulcanization agent, and the mixture was kneaded bya twin-roll to obtain an insulator composition for a cathode ray tube.

This insulator composition was processed into a tape shape having athickness of 1 mm and width of 1.5 mm by an extruder and punched out tothe shape of FIG. 6 using a punch to obtain an electrical insulator. Theloss of the insulator composition was 40 percent. Subsequently, theadhering portion of the electrical insulator was adhered to the stembase, then the electrical insulator was pressed to straighten out itsshape, the folding portion extending to the tip holder of the stem wasfolded to the inside surface of the tip holder, then the stem base wasattached to the stem of the cathode ray tube, this was pressed by apressing force of 1 MPa, and the entire cathode ray tube was heated in aheating chamber at 100° C. for 10 minutes to bond and secure the stembase to the stem to achieve insulation between the high voltage use stempins. The bonding strength of the stem base to the stem at this time wasa low 0.7 MPa. Further, voltage was applied across the high voltage usestem pins to test the insulation withstand voltage. As a result, theinsulation breakdown voltage was 15 kV. A decline in the insulationproperty was seen comparing with the above Examples 1 and 2.

It was confirmed from the results of the above that, according to themethod of insulating a cathode ray tube and the insulator compositionfor a cathode ray tube of the embodiments, it is possible to obtain anelectrical insulator without loss of the insulator composition andpossible to realize a cathode ray tube having an improved bondingstrength of the stem and the stem base and an improved insulationproperty between the stem pins.

Summarizing the advantageous effects of the invention, as explainedabove, according to the method of insulating a cathode ray tubeaccording to the present embodiment, since an electrical insulator isobtained by transfer molding of the electrical insulator composition, itis possible to produce an electrical insulator without loss byefficiently using the electrical insulator composition. Further, sinceit is possible to easily form an electrical insulator into a shapematching with the complex-shaped stem and stem base of a cathode raytube by the transfer molding and further since the electrical insulatoris adhered to the stem base in the state with the portion of theelectrical insulator extending toward the tip holder is folded to theinside surface of the tip holder prior to attaching the stem base to thestem, it is possible to attach the stem base to the stem without airentrainment. Accordingly, a cathode ray tube wherein the stem and thestem base are strongly bonded and the insulation property between thehigh voltage use stem pins is high can be realized.

Further, according to the electrical insulator composition for a cathoderay tube according to the present invention, by using a siliconecompound, it is possible to obtain an electrical insulator compositionhaving a good releasability from a transfer mold, easy to be molded intoa complex shape, easy to handle, and otherwise well suited to transfermolding and further having an excellent rubber strength, a property ofcuring at a suitable curing rate, and an excellent insulation property.Accordingly, this electrical insulator composition becomes extremelyeffective for realization of a cathode ray tube improved in the bondingstrength of the stem and the stem base and improved in the insulationproperty between the high voltage use stem pins by working the method ofinsulating a cathode ray tube of the above invention.

Note that the present invention is not limited to the above embodimentsand includes modifications within the scope of the claims.

What is claimed is:
 1. A method of insulating a cathode ray tube forinsulation between stem pins using an electrical insulator whenattaching to a stem, which is provided at the cathode ray tube and has atip and stem pins projecting therefrom, an insulating stem base, whichcomprises a base through which pin through holes are formed and hasprovided projecting from the front surface thereof a tip holder, in astate with the stem pins inserted through the pin through holes and thetip held in the tip holder, said method comprising the steps of:moldingan electrical insulator composition comprising an uncured self-adhesivesilicone rubber into a predetermined sheet shape by using a transfermold to obtain an electrical insulator, arranging the electricalinsulator in a state extending from the positions of the pin throughholes on the back of the base of the stem base to the tip holder andadhering it to the back of the base, folding back the portion of theelectrical insulator extending to the tip holder to the inside surfaceof the tip holder, and attaching the stem base to the stem.
 2. A methodof insulating a cathode ray tube as set forth in claim 1, furthercomprising, between the step of adhering the electrical insulator andthe step of folding back the extending portion of the electricalinsulator, a step of pressing the electrical insulator to straighten outits shape.